The present invention relates to a novel (poly)oxyalkylene block silyl ester copolymer. More particularly, the present invention is concerned with a (poly)oxyalkylene block silyl ester copolymer which, when used as a vehicle of coating composition or paint, enables forming a coating having excellent transparency and being excellent in foul removing performance, i.e., capability of easily removing foul from a coating surface.
Ship bottoms, underwater structures, fishing nets and the like are likely to have their appearance and function damaged by the adhesion to surface and propagation of various aquatic organisms including shellfishes such as oysters, hard-shelled mussels and barnacles, plants such as laver (seaweeds) and bacteria which is caused when they are exposed to water or seawater for a prolonged period of time.
In particular, when such an aquatic organism adheres to a ship""s bottom and propagates, it may occur that the surface roughness of the ship""s bottom is increased to thereby lower the speed of the ship and increase the fuel consumed by the ship. Removing the aquatic organism from the ship bottom takes thousands of man-hours, so that many labors and much time are needed for this work. Also, when bacteria adhere to, for example, an underwater structure and propagate and, further, slime (sludgy matter) adheres thereto to cause putrefaction, or when a large sticky organism adheres to the surface of an underwater structure of, for example, steel and propagates to thereby damage the coating for corrosion prevention provided on the underwater structure, there is the danger that damages such as deterioration of the strength and function of the underwater structure and thus marked shortening of the life thereof are invited.
In order to avoid the above damages, for example, an antifouling paint containing a copolymer of tributyltin methacrylate and methyl methacrylate or the like and cuprous oxide (Cu2O) has been applied to ship bottoms, etc. This copolymer of the antifouling paint is hydrolyzed in the seawater to thereby liberate organotin compounds such as bistributyltin oxide (tributyltin ether of the formula Bu3Snxe2x80x94Oxe2x80x94SnBu3 wherein Bu is a butyl group) and tributyltin halides (Bu3SnX wherein X is a halogen atom), so that an antifouling effect is exerted. Furthermore, the copolymer hydrolyzate per se has water-solubility and thus is dissolved in the seawater, as a result, no residue of hydrolyzate is left on the surface of the ship bottom coating, and then the new paint film surface in which the copolymer is not hydrolyzed is exposed to maintain the antifouling effect for long. The antifouling paint having such a performance is called as xe2x80x9chydrolyzable self-polishing paintxe2x80x9d.
However, the above organotin compounds are so highly toxic that apprehensions are being entertained with respect to marine pollution, occurrence of anomalous fish and anomalous shellfish and adverse effects on ecosystem through food chain. Therefore, the development of a nonstannic antifouling paint having excellent antifouling properties is desired as a substitute therefor.
For example, antifouling paints based on silyl esters as described in Japanese Patent Laid-open Publication Nos. 4(1992)-264170 (reference (1)), 4(1992)-264169 (reference (2)) and 4(1992)-264168 (reference (3)) can be mentioned as the above nonstannic antifouling paint. However, these antifouling paints have problems that not only are their antifouling capabilities poor but also cracking and peeling are likely to occur as pointed out in Japanese Patent Laid-open Publication Nos. 6(1994)-157941 (reference (4)) and 6(1994)-157940 (reference (5))
Further, Japanese Patent Laid-open Publication No. 2(1990)-196869 (reference (6)) teaches an antifouling paint comprising a blocked acid-functionality copolymer (A) which is obtained by copolymerizing trimethylsilyl methacrylate, ethyl methacrylate and methoxyethyl acrylate in the presence of an azo initiator and which contains carboxyl groups blocked with trimethylsilyl groups and a polycationic compound (B). However, the coating film obtained from the antifouling paint has a drawback in that the cracking resistance thereof is not fully satisfactory.
Published Japanese Translation of PCT Patent Applications from Other States, No. 60(1985)-500452 (reference (7)) and Japanese Patent Laid-open Publication No. 63(1988)-215780 describe a resin for antifouling paint which is obtained by copolymerizing a vinyl monomer having an organosilyl group, such as a trialkylsilyl ester of (meth)acrylic acid, with another vinyl monomer and which has a number average molecular weight of 3000 to 40,000. It is further described that the resin can be blended with an organic water binder such as trimethyl orthoformate, an antifouling agent such as cuprous oxide and a pigment such as red iron oxide. However, as described in the above Japanese Patent Laid-open Publication No. 6(1994)-157940 (reference (5)), this resin for antifouling paint has drawbacks in that it is likely to gelate during the storage thereof and that the coating film formed from the antifouling paint is poor in cracking and peeling resistances.
Japanese Patent Publication No. 5(1993)-32433 corresponding to the above Published Japanese Translation of PCT Patent Applications from Other States, No. 60(1985)-500452 (reference (7)) discloses an antifouling paint comprising a poison (a) and a polymer binder (b) having a repeating unit of the formula (xe2x80x94CH2xe2x80x94CX(COOR)xe2x80x94(B)xe2x80x94 wherein X is H or CH3, R is SiRxe2x80x23 or Si(ORxe2x80x2)3 in which Rxe2x80x2 is an alkyl group, etc. and B is an ethylenically unsaturated monomer residue), which polymer binder has a specified hydrolysis rate. Further, it is described that the antifouling paint can contain a solvent, a water-sensitive pigment component, an inert pigment, a filler and a retarder. However, the coating film obtained from the antifouling paint described in the publication has a drawback in that its cracking resistance is poor.
Japanese Patent Laid-open Publication No. 7(1995)-18216 (reference (8)) discloses a coating composition comprising as principal components a polymer (A) from an organosilicon-containing monomer A having in its molecule a triorganosilicon ester group represented by the formula xe2x80x94COOxe2x80x94SiR1R2R3 (wherein each of R1, R2 and R3 is, for example, an alkyl group having 1 to 18 carbon atoms) and copper or a copper compound (B), which coating composition contains as an essential component other than the components (A) and (B) a silicon compound having an alkoxy group (C) represented by the formula: 
wherein each of R4, R5 and R6 represents, for example, a hydrogen atom, or an alkoxy group or cycloalkoxy group having 1 to 18 carbon atoms; R7 represents, for example, an alkyl group having 1 to 18 carbon atoms; and n is an integer of 1 to 3. In the publication, it is described that a copolymer AB obtained by copolymerizing the above organosilicon-containing monomer A and a vinyl monomer copolymerizable therewith B may be contained in the coating composition. As the monomer B, there are mentioned (meth)acrylic esters such as methyl (meth)acrylate, ethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate.
However, the coating film obtained from the coating composition described in the publication has a drawback in that it is inferior in cracking resistance and antifouling properties, in particular, antifouling properties in highly fouling environment. The expression xe2x80x9cin highly fouling environmentxe2x80x9d used herein means such situations that a ship or an underwater structure is allowed to stand still in a nutrious sea area such as an inland sea or other like sea area, or, with respect to a ship, service and anchorage are repeated frequently or navigation is conducted at a speed as low as about 10 knots or less.
Japanese Patent Laid-open Publication No. 7(1995)-102193 (reference (9)) discloses a coating composition comprising as essential components an antifouling agent and a copolymer obtained from a monomer mixture containing monomer A represented by the formula Xxe2x80x94SiR1R2R3 (wherein R1, R2 and R3 all represent a group selected from among alkyl and aryl groups and may be identical with or different from each other, and X represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy or a fumaroyloxy group), and monomer B represented by the formula Yxe2x80x94(CH2CH2O)nxe2x80x94R4 (wherein R4 represents an alkyl or an aryl group, Y represents an acryloyloxy or a methacryloyloxy group, and n is an integer of 1 to 25). As the antifouling agent, there are mentioned inorganic compounds such as cuprous oxide, copper powder and other copper compounds, zinc sulfate and zinc oxide, and further mentioned organometallic compounds such as oxine copper and other organocopper compounds, organonickel compounds, and zinc pyrithione and other organozinc compounds. However, there is no suggestion on a polymer having a (poly)oxyalkylene block structure and containing an organosilyl ester group in the publication, and, further, the paint described in the publication has a problem of being inferior in antifouling properties, in particular, antifouling properties in highly fouling environment.
Japanese Patent Laid-open Publication No. 8(1996)-199095 (reference (10)) discloses a coating composition comprising as essential components an antifouling agent and a copolymer obtained from a monomer mixture containing the above monomer A represented by the formula Xxe2x80x94SiR1R2R3 described in Japanese Patent Laid-open Publication No. 7(1995)-102193 and monomer B represented by the formula Yxe2x80x94(CH(R4))xe2x80x94(OR5) (wherein R4 represents an alkyl group; R5 represents an alkyl or a cycloalkyl group; and Y represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy or a fumaroyloxy group), optionally together with a vinyl monomer C copolymerizable with the monomers A and B. As the vinyl monomer C, there are mentioned, for example, acrylic esters, methacrylic esters, styrene and vinyl acetate. Moreover, as the antifouling agent, there are mentioned inorganic compounds such as cuprous oxide, copper powder and other copper compounds, zinc sulfate and zinc oxide, and further mentioned organometallic compounds such as oxine copper and other organocopper compounds, organonickel compounds, and zinc pyrithione and other organozinc compounds.
Japanese Patent Laid-open Publication No. 8(1996)-269388 (reference (11)) discloses a coating composition comprising, as essential components, bis(2-pyridinethiol-1-oxide) copper salt (copper pyrithione) and a copolymer obtained from a monomer mixture containing monomer A represented by the formula Xxe2x80x94SiR1R2R3 (wherein R1, R2 and R3 all represent a hydrocarbon group having 1 to 20 carbon atoms and may be identical with or different from each other, and X represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy, a fumaroyloxy or an itaconoyloxy group), and monomer B represented by the formula Yxe2x80x94(CH2CH2O)nxe2x80x94R4 (wherein R4 represents an alkyl or an aryl group; Y represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy, a fumaroyloxy or an itaconoyloxy group; and n is an integer of 1 to 25). For example, dimethyl-t-butylsilyl acrylate is mentioned as the monomer A. As the antifouling agent, there are mentioned inorganic compounds such as cuprous oxide, copper powder and other copper compounds, zinc sulfate and zinc oxide, and further mentioned organometallic compounds such as oxine copper and other organocopper compounds, organonickel compounds, and zinc pyrithione and other organozinc compounds. Furthermore, for example, rosin and rosin derivatives are mentioned as a leaching rate regulator which can be added to the coating composition.
Japanese Patent Laid-open Publication No. 8(1996)-269389 (reference (12)) discloses a coating composition comprising an antifouling agent and a copolymer copolymerized a monomer mixture containing an unsaturated monomer A having a triorganosilyl group and a monomer B represented by any of the following formulae.
The monomer B can be:
monomer having a tertiary amino group, represented by the formula CH2xe2x95x90CR4COOR5xe2x80x94NR6R7 (wherein R4 represents H or CH3; R represents an alkylene group; and R6 and R7 represent alkyl groups and may be identical with or different from each other),
monomer containing a quaternary ammonium salt, represented by the formula CH2xe2x95x90CR8COOR9xe2x80x94NR10R11R 12(Y) (wherein R8 represents H or CH3; R9 represents an alkylene group; R10 to R12 represent alkyl groups and may be identical with or different from each other; and Y represents a halogen atom),
monomer containing a nitrogenous heterocycle, represented by the formula CH2xe2x95x90CHxe2x80x94Z (wherein Z represents a group comprising a nitrogenous heterocycle),
monomer having in its molecule an alkoxy group or an aryloxyalkylene glycol group, represented by the formula CH2xe2x95x90CR13COO(R14O)m(R15O)n(R16O)oxe2x80x94R17 (wherein R13 represents H or CH3; R14 represents an ethylene group; R15 represents an alkylene group having 3 carbon atoms; R16 represents an alkylene group having 4 carbon atoms; R17 represents an alkyl group or aryl group; and each of m, n and o is an integer of 0 or greater, provided that n and o are not simultaneously 0),
(meth)acrylamide represented by the formula CH2xe2x95x90CR18CONR19R20 (wherein R18 represents H or CH3; and R19 and R20 represent alkyl groups and may be identical with or different from each other),
(meth)acrylamide having a nitrogenous cyclic hydrocarbon group, represented by the formula CH2xe2x95x90CR21CON( )Q (wherein R21 represents H or CH3; and N( )Q is a nitrogen-containing nitrogen group wherein, for example, O, N or S may be contained in Q),
(meth)acrylic ester containing a furan ring, represented by the formula CH2xe2x95x90CR23COOCH2xe2x80x94T (wherein R23 represents H or CH3; and T represents a furan ring or a tetrahydrofuran ring), or
CH2xe2x95x90CHxe2x80x94CN.
Further, as an optional component copolymerizable with the above monomers A and B, there are mentioned various copolymerizable monomers such as acrylic acid, ethyl acrylate, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.
In the Example portion, there are mentioned, for example, a copolymer from tri-n-butylsilyl acrylate (TBSA), diethylaminoethyl methacrylate (DEAEMA) and methyl methacrylate (MMA) and a copolymer from tri-n-butylsilyl acrylate (TBSA), N,N-dimethylacrylamide (DMAA) and methyl methacrylate (MMA). However, there is no suggestion on a copolymer having a (poly)oxyalkylene block structure and containing an organosilyl ester group in the publication.
Still further, as a component which can be added to the coating composition, there are mentioned the same antifouling agents as described in the above Japanese Patent Laid-open Publication No. 8(1996)-269388.
Japanese Patent Laid-open Publication No. 8(1996)-269390 (reference (13)) discloses a coating composition comprising:
a polymer from monomer A represented by the formula Xxe2x80x94SiR1R2R3 (wherein R1, R2 and R3 all represent groups selected from among alkyl and aryl groups and may be identical with or different from each other, and X represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy, a fumaroyloxy or an itaconoyloxy group),
a polymer from monomer B represented by the formula Yxe2x80x94(CH2CH2O)nxe2x80x94R4 (wherein R4 represents an alkyl or an aryl group; Y represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy, a fumaroyloxy or an itaconoyloxy group; and n is an integer of 1 to 25), and
an antifouling agent. As the antifouling agent, there are mentioned the same antifouling agents as described in the above Japanese Patent Laid-open Publication No. 8(1996)-269388. Further, as a component which can be added to the coating composition, there are mentioned, for example, resins such as rosin and antisetting agents.
Japanese Patent Laid-open Publication No. 8(1996)-277372 (reference (14)) discloses a coating composition comprising a triphenylboron pyridine complex and a copolymer from a monomer mixture containing the monomer A represented by the formula Xxe2x80x94SiR1R2R3 described in the above Japanese Patent Laid-open Publication No. 8(1996)-269388 (reference (11)) and the monomer B represented by the formula Yxe2x80x94(CH2CH2O)nxe2x80x94R4 described in the same reference, and further comprising a resin component and a marine organism adhesion inhibitor which consist only of a nonmetallic polymer and a nonmetallic organic inhibitor, respectively. Further, for example, rosin and rosin derivatives are mentioned as a leaching rate regulator which can be added to the coating composition.
Japanese Patent Laid-open Publication No. 10(1998)-30071 (reference (15)) discloses a coating composition comprising at least one rosin compound (A) consisting of rosin, a rosin derivative or a rosin metal salt, a polymer having an organosilyl ester group (B) consisting of a polymer from at least one monomer M represented by the formula Xxe2x80x94SiR1R2R3 (wherein R1, R2 and R3 all represent groups selected from among alkyl and aryl groups and may be identical with or different from each other, and X represents an acryloyloxy, a methacryloyloxy, a maleinoyloxy, a fumaroyloxy, an itaconoyloxy or a citraconoyloxy group), and/or a polymer from the above at least one monomer M and at least one other polymerizable monomer, and an antifouling agent (C). Further, as another monomer acting as an optional component copolymerizable with the above monomer M, there are mentioned, for example, acrylic acid, methyl acrylate, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. However, there is no suggestion on a copolymer having a (poly)oxyalkylene block structure and containing an organosilyl ester group in the publication.
As the antifouling agent, there are mentioned the same antifouling agents as described in the above Japanese Patent Laid-open Publication No. 8(1996)-269388 Further, as a component which can be added to the coating composition, there are mentioned, for example, pigments, chlorinated paraffin and antisetting agents.
However, in these references (9) to (15), there is no suggestion on a copolymer having a (poly)oxyalkylene block structure and containing an organosilyl ester group. Further, with the use of coating compositions described in these references, the obtained coating film is either poor in cracking resistance, or unsatisfactory from the viewpoint of a balance of cracking resistance, peeling resistance (coating adherence), antifouling performance or antifouling properties, in particular, antifouling properties in highly fouling environment, long-term antifouling properties and self-polishing properties.
Further, for example, 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate are mentioned as a copolymerizable optional component in Japanese Patent Publication No. 5(1993)-82865 (reference (16)). Still further, silyl (meth)acrylate copolymers are described in Japanese Patent Laid-open Publication No. 9(1997)-48947 (reference (17)), Japanese Patent Laid-open Publication No. 9(1997)-48948 (reference (18)), Japanese Patent Laid-open Publication No. 9(1997)-48949 (reference (19)), Japanese Patent Laid-open Publication No. 9(1997)-48950 (reference (20)), Japanese Patent Laid-open Publication No. 9(1997)-48951 (reference (21)), Japanese Patent Publication No. 5(1993)-32433 (reference (22)), U.S. Pat. No. 4,593,055 (reference (23)), Japanese Patent Laid-open Publication No. 2(1990)-1968669 (reference (24)) and WO 91/14743 (reference (25)). However, in these references (16) to (25), there is no suggestion on a copolymer having a (poly)oxyalkylene block structure and containing an organosilyl ester group. Further, with the use of antifouling paints based on copolymers described in these references (16) to (25), the obtained coating film is either poor in cracking resistance, or has room for further improvement from the viewpoint of a balance of cracking resistance, peeling resistance (coating film adherence), antifouling performance or antifouling properties, in particular, antifouling properties in highly fouling environment, long-term antifouling properties and self-polishing properties.
Japanese Patent Laid-open Publication No. 63(1988)-215780 (reference (26)) describes copolymers formed using, for example, methyl methacrylate, n-butyl methacrylate and acrylamide as copolymerization components, and further describes antifouling paints containing the above copolymers and cuprous oxide. These antifouling paints have the same drawbacks as those of the antifouling paints of the above references.
WO 96/03465 (reference (27)) describes star-type polymers obtained using tri- to octa-functional mercapto compounds. It is described that these polymers have such a low viscosity as to enable preparation of a paint of high solid content, and that the tendency thereof toward viscosity increase or gelation during storage is low. Moreover, the use of an unsaturated carboxylic acid silyl ester as a monomer is described in the WO 96/03465. However, there is no suggestion on a copolymer having an organosilyl ester group, which copolymer has such a block structure as, like a (poly)oxyalkylene, has hydrophilicity and can improve the antifouling performance of antifouling paint, and at least an AB type or ABA type block copolymer is not taught at all in the reference.
The present invention has been made with a view toward solving the above problems of the prior art. It is an object of the present invention to provide a copolymer for antifouling paint which enables forming such an antifouling coating film as exhibits less cracking tendency, excellent adherence so as to ensure less peeling tendency and desirably controlled hydrolysis rate so as to be extremely excellent in antifouling properties in highly fouling environment and long-term antifouling properties as antifouling performance (antifouling activity). It is another object of the present invention to provide an antifouling coating composition which can form an antifouling coating film exhibiting less cracking tendency, excellent adherence so as to ensure less peeling tendency and desirably controlled hydrolysis rate so as to be extremely excellent in antifouling properties in highly fouling environment and long-term antifouling properties.
It is further objects of the present invention to provide an antifouling coating film formed from the above antifouling coating composition, to provide an antifouling method effected with the use of the above antifouling coating composition, and to provide a hull or underwater structure covered with the above antifouling coating film.
The (poly)oxyalkylene block silyl ester copolymer of the present invention comprises silyl ester copolymer block units (A) and block units (B),
the silyl ester copolymer block units (A) comprising:
(a) component units derived from a polymerizable unsaturated carboxylic acid silyl ester, and
(b) polymerizable unsaturated monomer units other than the component units (a),
the block units (B) derived from a mercapto compound represented by the formula: 
wherein R1 represents a hydrocarbon group or ether-bond-containing hydrocarbon group having a valency of 1 or higher and having 1 to 30 carbon atoms; R2 represents a bivalent hydrocarbon group having 1 to 30 carbon atoms or a group of the formula xe2x80x94CH(R3)xe2x80x94wherein R3 represents a group of the formula R4xe2x80x94Oxe2x80x94R5, R4 representing a bivalent hydrocarbon group having 1 to 30 carbon atoms, and R5 representing a monovalent hydrocarbon group having 1 to 30 carbon atoms; X represents: 
n is an integer of 1 to 5; m is an integer of 1 to 100; l is an integer of 1 to 5; k is an integer of 0 to 100; a is an integer of 0 or 1; j is an integer of 1 to 50; and i is the valency of R1.
The component units derived from a polymerizable unsaturated carboxylic acid silyl ester (a) preferably contain component units (a-1) derived from a silyl (meth)acrylate are represented by the formula:
xe2x80x94CH2xe2x80x94CR(COOSiRaRbRc)xe2x80x94xe2x80x83xe2x80x83(I) 
wherein R represents a hydrogen atom or a methyl group; and Ra, Rb and Rc may be identical with or different from each other and each represent a linear alkyl group, a branched alkyl group, a cycloalkyl group, a substituted or unsubstituted phenyl group or a trimethylsilyoxy group.
In the formula (I), it is preferred that at least one of the Ra, Rb and Rc represent a branched alkyl group or a cycloalkyl group.
Also, the component units derived from a polymerizable unsaturated carboxylic acid silyl ester (a) preferably comprise:
silyl (meth)acrylate component units (a-2) of the formula:
xe2x80x94CH2xe2x80x94CR(COOSiR11R 12R13)xe2x80x94xe2x80x83xe2x80x83(II) 
wherein R represents a hydrogen atom or a methyl group; each of R11 and R12 independently represents a linear alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted phenyl group, or a trimethylsilyloxy group; and R13 represents an alkyl group having 1 to 18 carbon atoms which may have a ring structure or branch, a substituted or unsubstituted phenyl group having 6 to 10 carbon atoms, or a trimethylsilyloxy group, and
silyl (meth)acrylate component units (a-3) of the formula:
xe2x80x94CH2xe2x80x94CR(COOSiR14R15R16)xe2x80x94xe2x80x83xe2x80x83(III) 
wherein R represents a hydrogen atom or a methyl group; each of R14 and R15 independently represents a branched alkyl or cycloalkyl group having 3 to 10 carbon atoms; and R16 represents a linear alkyl group having 1 to 10 carbon atoms, a branched alkyl or cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted phenyl group having 6 to 10 carbon atoms, or a trimethylsilyloxy group.
It is preferred that the polymerizable unsaturated monomer units (b) other than the component units (a) comprise component units (b-1) derived from an acrylic unsaturated monomer containing a polar group.
Preferably, the component units (b-1) derived from an acrylic unsaturated monomer containing a polar group have component units derived from an acrylic unsaturated monomer containing at least one polar group selected from the group consisting of a hydroxyl group, a hydroxyalkyl group, an alkoxyl group, a polyoxyalkylene group, an alkylpolyoxyalkylene group, an amino group, an N-substituted amino group, an amido group, an N-substituted amido group, an epoxy group, an oxolane group, an oxetane group, an oxirane group, a tetrahydrofurfuryl group and a morpholino group.
The use of the above (poly)oxyalkylene block silyl ester copolymer according to the present invention as a vehicle of antifouling paint enables providing an antifouling coating composition which enables forming such an antifouling coating film exhibiting less cracking tendency, excellent adherence so as to ensure less peeling tendency and desirably controlled hydrolysis rate so as to be extremely excellent in antifouling properties in highly fouling environment and long-term antifouling properties, which antifouling coating film is further excellent in a balance of these properties.
The antifouling coating composition of the present invention comprises a (poly)oxyalkylene block silyl ester copolymer, the (poly)oxyalkylene block silyl ester copolymer comprising silyl ester copolymer block units (A-1) and block units (A-2),
the silyl ester copolymer block units (A-1) comprising:
(a) component units derived from a polymerizable unsaturated carboxylic acid silyl ester, and
(b) polymerizable unsaturated monomer units other than the component units (a),
the block units (A-2) derived from a mercapto compound represented by the formula: 
wherein R1 represents a hydrocarbon group or ether-bond-containing hydrocarbon group having a valency of 1 or higher and having 1 to 30 carbon atoms; R2 represents a bivalent hydrocarbon group having 1 to 30 carbon atoms or a group of the formula xe2x80x94CH(R3)xe2x80x94wherein R3 represents a group of the formula R4xe2x80x94Oxe2x80x94R5, R4 representing a bivalent hydrocarbon group having 1 to 30 carbon atoms, and R5 representing a monovalent hydrocarbon group having 1 to 30 carbon atoms; X represents: 
n is an integer of 1 to 5; m is an integer of 1 to 100; l is an integer of 1 to 5; k is an integer of 0 to 100; a is an integer of 0 or 1; j is an integer of 1 to 50; and i is the valency of R1.
The component units derived from a polymerizable unsaturated carboxylic acid silyl ester (a) preferably contain component units (a-1) derived from a silyl (meth)acrylate of the formula:
xe2x80x94CH2xe2x80x94CR(COOSiRaRbRc)xe2x80x94xe2x80x83xe2x80x83(I) 
wherein R represents a hydrogen atom or a methyl group; and Ra, Rb and Rc may be identical with or different from each other and each represent a linear alkyl group, a branched alkyl group, a cycloalkyl group, a substituted or unsubstituted phenyl group or a trimethylsilyloxy group.
In the formula (I), it is preferred that at least one of the Ra, Rb and Rc represent a branched alkyl group or a cycloalkyl group.
Also, the component units derived from a polymerizable unsaturated carboxylic acid silyl ester (a) preferably comprise:
silyl (meth)acrylate component units (a-2) of the formula:
xe2x80x94CH2xe2x80x94CR(COOSiR11R12R13)xe2x80x94xe2x80x83xe2x80x83(II) 
wherein R represents a hydrogen atom or a methyl group; each of R11 and R12 independently represents a linear alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted phenyl group, or a trimethylsilyloxy group; and R13 represents an alkyl group having 1 to 18 carbon atoms which may have a ring structure or branch, a substituted or unsubstituted phenyl group having 6 to 10 carbon atoms, or a trimethylsilyloxy group, and
silyl (meth)acrylate component units (a-3) of the formula:
xe2x80x94CH2xe2x80x94CR(COOSiR14R15R16)xe2x80x94xe2x80x83xe2x80x83(III) 
wherein R represents a hydrogen atom or a methyl group; each of R14 and R15 independently represents a branched alkyl or cycloalkyl group having 3 to 10 carbon atoms; and R16 represents a linear alkyl group having 1 to 10 carbon atoms, a branched alkyl or cycloalkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted phenyl group having 6 to 10 carbon atoms, or a trimethylsilyloxy group.
Preferably, the polymerizable unsaturated monomer units (b) other than the component units (a) comprise component units (b-1) derived from an acrylic unsaturated monomer containing a polar group.
It is preferred that the component units (b-1) derived from an acrylic unsaturated monomer containing a polar group have at least one polar group selected from the group consisting of a hydroxyl group, a hydroxyalkyl group, an alkoxyl group, a polyoxyalkylene group, an alkylpolyoxyalkylene group, an amino group, an N-substituted amino group, an amido group, an N-substituted amido group, an epoxy group, an oxolane group, an oxetane group, an oxirane group, a tetrahydrofurfuryl group and a morpholino group.
The antifouling coating composition of the present invention preferably further comprises an antifouling agent (B).
Also, the antifouling coating composition of the present invention preferably further comprises zinc oxide (C).
Moreover, it is preferred that the antifouling coating composition of the present invention further comprise an inorganic dehydrating agent (D).
It is also preferred that the antifouling coating composition of the present invention further comprise a leaching accelerating component (E).
The antifouling coating film of the present invention is formed from the above antifouling coating composition of the present invention.
The method of rendering antifouling a marine vessel, an underwater structure, a fishing gear or a fishing net according to the present invention comprises applying the above antifouling coating composition of the present invention to a base surface of a marine vessel, an underwater structure, a fishing gear or a fishing net and drying the applied antifouling coating composition so that a formed antifouling coating film covers the base surface.
The marine vessel, underwater structure, fishing gear or fishing net according to the present invention has a surface covered with the above antifouling coating film formed from the antifouling coating composition of the present invention.
According to the present invention, there is provided an antifouling coating composition which, because of the containing of specified (poly)oxyalkylene block silyl ester copolymer, enables forming such an antifouling coating film as exhibits less cracking tendency, excellent adherence so as to ensure less peeling tendency and desirably controlled hydrolysis rate so as to be excellent in antifouling performance (antifouling activity), antifouling properties, in particular, antifouling properties in highly fouling environment and long-term antifouling properties, which antifouling coating film is further excellent in a balance of these properties.